Orthopaedic implants, including for instance knee implants, can be modular in nature and include several components. For instance, many knee implants include a femoral implant and a tibial implant. The tibial implant may include a base tibial component and one or more inserts. After bone resectioning, the tibial component is positioned on the patient's tibia and the femoral component is positioned on the patient's femur. The tibial insert is secured to or captured by the tibial component, and includes a superior surface for contact with one or two (depending on the type of femoral implant) condylar surfaces of the femoral component (or the native femoral condyles). In use, the condylar surfaces of the femoral component and/or native femur will articulate on the superior surface of the tibial insert as the knee joint flexes and extends.
Tibial inserts may be either fixed or rotatable. A rotatable tibial insert rotates with respect to the tibial component (which is fixedly secured to the tibia) as the knee joint flexes and extends. On the other hand, a fixed tibial insert is not intended to rotate with respect to the tibial component when the knee joint flexes and extends. The type of implant chosen for a particular patient, including whether a fixed or rotating tibial insert is used, depends on a number of factors, including the condition of the patient's bones, ligamenture and other anatomy.
The components of a knee implant are subject to large loads and other forces in vivo that are applied over many cycles throughout the implant's useful life. Accordingly, it is important that the components of the tibial implant, including the tibial component and the tibial insert, be appropriately coupled to one another such that they do not separate or otherwise move in unintended manners once implanted in the patient.
Prior systems of coupling the components have several problems. First, some prior systems use coupling mechanisms that are “exposed” in that when the knee joint is in flexion, edges, protrusions or other surfaces of the coupling mechanism contact or impinge on the patient's surrounding anatomy. Such contact or impingement may be painful to the patient, may destroy or damage the ligamenture, bone and/or other anatomy, or may damage the locking component. Second, many prior systems do not provide adequate constraints against movement (both rotational and vertical) of tibial inserts with respect to their associated tibial components, especially as the implant is cycled numerous of times. In some instances, prior systems can fail when the tibial insert “spins outs,” “pulls out,” or otherwise becomes dislocated with respect to the tibial component. Spin out refers to excessive rotation of the tibial insert (particularly for rotatable tibial inserts) such that the tibial insert becomes improperly oriented within the knee joint. Pull out refers to vertical separation between the tibial insert and the tibial component. Third, prior systems with fixed tibial inserts, in some instances, may undesirably allow at least some rotation of the fixed insert. Fourth, prior systems with fixed tibial inserts may use fasteners to secure the insert to the tibial component that may loosen and back out, thus un-coupling the insert from the tibial component.
Thus, there is a need in some instances for an orthopaedic implant that includes structure to couple a tibial insert to a tibial component, but that avoids contact with the patient's ligamenture, bone and other surrounding anatomy.
There is a need in some instances for an orthopaedic implant that minimizes excessive or undesirable rotation between the tibial insert and the tibial component.
There is a need in some instances for an orthopaedic implant that avoids vertical separation of the tibial insert from the tibial component.
There is a need in some instances for improved fasteners that will not loosen or back out of the tibial insert.
Finally, there is a need in some instances for a tibial component that may be used interchangeably with either a fixed tibial insert or a rotatable tibial insert.